I didn't mind the penultimate one so much (assuming you mean the Cosmic Egg), but yeah, the final is just a mess. Boring enemies (though fitting considering it's Law on steroids), everything looks the same, there are teleporters everywhere and the music just drones on and on.almost done with smt4a and the final two dungeons are fucking awful.
penultimate one has jack for demon fusion options and everything looks the same.
final one is the same but you cant even talk to any of the demons and its even worse looking and more annoying to get around.
they keep giving me relics and there are no shops here.
Shame because the rest of the game is so good. I made it past King Frost tonight on my NG+ playthrough. I had forgotten how much of an asshole he was to fight. Though in the end it turned out I could shut him down completely with just one skill: Magaon, which removes smirk.